The invention relates generally to piezoelectric control valves and more specifically to an automatically compensating piezoelectric control valve.
A piezoelectric control valve for controlling the motor fuel injection via an injection valve is shown in U.S. Pat. No. 3,501,099 in FIG. 5. Since the working stroke of a piezoceramic column, at a justifiable overall length, is relatively small for physical reasons, this control valve, to increase the valve stroke, has a stroke transmission which is formed by a tappet cylinder. The tappet cylinder can be moved by the piezoelectric actuator, interacting with a valve piston of the valve via a fluid located in a chamber. The end face of the valve piston is made smaller than the end face of the tappet cylinder.
Moreover, on account of the rough environment in which the piezoelectric control valves are used, hydraulic forces, temperature changes and also depolarizing actions can cause changes in length of the piezoceramic columns, but with the working stroke being fully maintained.
From this it is apparent that at such a relatively small working stroke, the control valve arrangement will react very sensitively to a setting action of the piezoceramic and at the control valve, the valve gap must be made exactly true to size so that the gap can be closed or opened at a given working stroke.
Thus, with regard to compensation of play, a valve drive for controlling internal-combustion engines has been disclosed in German Offenlegungsschrift No. 3,418,707. A hydraulic play-compensation element is arranged in the direction of the lines of force between a cam of a cam shaft and a valve piston of a gas change valve in order to ensure that play occurring at the cam and/or at the cup-type tappet interacting with it on account of wear phenomena is always compensated.
Thus, it is an object of the invention to make, while maintaining the working stroke, a piezoelectric control valve, having a stroke transmission, that automatically compensates to maintain a constant valve stroke for any changes in length which may occur in the piezoelectric actuator forming the reference system.
These and other objects are achieved by providing a hydraulic play-compensation device connect to a fluid chamber between a valve piston which moves a control valve to open an injection valve and a tappet cylinder which is moved by the piezoelectric actuator to equalize pressure in the chamber resulting from changes in volume of the chamber during the return stroke. The relation ship between the valve piston and the tappet cylinder produces the stroke transmission, The hydraulic play-compensation element includes a spring loaded ball or check valve connected to the stroke transmission fluid chamber to create a path allowing refilling of the stroke transmission fluid chamber when the stroke of the tappet cylinder has been extended in the return direction because of a shortening of the piezoelectric drive element. Once the pressures are equalized, the ball valve closes thereby compensating the piezoelectric control valve. Small restrictive passages or gaps are Parallel to the ball valve to relieve high pressure in the stroke transmission fluid chamber which results from a reduced stroke of the tappet cylinder produced by an increase in the length of the piezoelectric actuator. The hydraulic play-compensation element is operable with Piezoelectric control valves wherein the piezoelectric actuator and the valve body move in the same or opposite directions.
Other objects, advantages and novel features of the Present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.